A number of commercial and industrial processes involve particulate or granular material. In some processes the moisture content of the particulate or granular material needs to be lowered before the material can be used in the process. An example is in the plastics field involving the use of plastic resins. The plastic resins may be initially granular materials produced in pellets. The plastic resin pellets may be processed by extrusion or other means in which the pellets are heated and molded or extruded into a desired shape. Many such plastic resin pellets have an affinity for water. Such hydroscopic particulate material cannot be properly processed by, for example, molding or extrusion. The heating in the molding or extrusion process can cause moisture in the pellets to vaporize creating imperfections in the final desired product. Other particulate or granular material may be produced having a moisture content that is too high for use in processes involving heating in which the vaporization of the moisture may interfere with the production of the final desired product. It is, therefore, desirable to dry such material before using it in such processes.
Conventional dryer hoppers for drying particulate material, particularly for drying polymer resin particulate material, suffer from a number of disadvantages. They typically consist of a vertically staged cylindrical housing. Particulate material to be dried is provided through the top of the housing and allowed to fall through the housing by gravity. Drying air is typically introduced into the hopper and may be passed into or up through the middle of the hopper. The upward flow of the drying air may be concentrated about the central portion or central vertical axis of the hopper on the belief that this is where the majority of the particulate material is concentrated. This can result in uneven drying of the particulate material. The material falling through the center of the housing may be dried to a greater extent than the material passing through the housing along or near the outer wall of the housing. Further, it tends to be inefficient, requiring greater airflow, and thus greater energy usage, than necessary to achieve sufficient drying of the material.